Before his death in 1996, noted astronomer Dr. Carl Sagan recorded a message to future explorers of Mars from his home in Ithaca, N.Y. In the quiet college town, far removed from the red planet, Sagan considered the possible reasons that would compel humankind to finally make its way to the neighboring orb, from necessity to innate human curiosity. But in the end, that didn't matter to him, because, as he said in his message: "… whatever the reason you're on Mars, I'm glad you're there. And I wish I was there with you."

Nearly 20 years later, Sagan's message still doesn't have an intended recipient. But we may be getting closer. Numerous rovers continue to prowl the surface of Mars, adding their data to the information gathered by satellites orbiting the planet. National programs in the United States, Europe and India all have Mars objectives. Private operations, including SpaceX and Mars One, intend to deploy manned missions to the fourth planet from the sun in just over a decade. NASA has set the 2030s as the target date for its own manned mission. And in the meantime, more revelations come to light.

Dark, narrow streaks, called recurring slope lineae, emanate from the walls of Garni Crater on Mars, in this view constructed from observations by the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter. (NASA/JPL-Caltech/Univ. of Arizona)

NASA recently announced that there is strong evidence that liquid water — likely very saline, and thus able to remain liquid at lower temperatures — flows intermittently on Mars. This evidence, the presence of hydrated salts gathered from the Mars Reconnaissance Orbiter, confirms speculation from 2011 that recurring slope lineae (what appear in satellite images as dark lines running down a Martian mountainside) are related to the presence of seasonal liquid water.

How the Waters of Mars Benefit Earth

The search for water is understandable; it is one of the necessities to sustain life as we understand it. Therefore, the detection of water is an important indicator of the potential for extraterrestrial life. (As Sagan famously said, "The universe is a pretty big place. If it's just us, seems like an awful waste of space.") The idea of water on Mars, or on other celestial bodies, is not new. We already know that Mars has vast amounts of water trapped in its polar ice caps. It seems like water is everywhere in our solar system these days, considering the discoveries of water on the icy moons of Jupiter (Europa, Ganymede) and Saturn (Enceladus) and on dwarf planet Ceres.

However, until recently, we somewhat arrogantly thought we had a monopoly on liquid water in the solar system. It turns out we were wrong. Recent evidence suggests that Ganymede's internal ocean may have more water than the Earth's Seven Seas put together. Our planet exists in the "Goldilocks zone," an optimal distance from the sun that allows biological life to flourish. In recognition of this, the Kepler Space Telescope scans other solar systems looking for planets similar to Earth. But the liquid water aspect, while interesting, is not necessarily the most important. In the very distant future, the presence of water (liquid or frozen) will be an important factor in potentially sustaining human life beyond our terrestrial bounds, but we could make technological advancements that allow us to better use the kind of frozen water we know exists on other planets and moons. And the benefits of water are not limited to simply fulfilling human biological needs; water found on Mars or elsewhere in the solar system could be used to produce fuel and electricity, enabling further exploration.

Manned trips to Mars are on the horizon, but such missions don't necessarily have to result in enduring human colonies. Even if the colonization of Mars doesn't occur in the lifetime of many of our readers, the discovery of water and other planetary science missions have very real benefits back on Earth. Planetary science missions require advanced technologies to complete their stated objectives, and many of these technological developments can be adapted for use at home. Materials science, additive manufacturing, agricultural technologies, radiation shielding, energy storage, water recycling and conservation are all poised to advance as a result of enhanced funding, research and development.

The dark, narrow streaks flowing downhill on Mars at sites such as this portion of Horowitz Crater are thought to be formed by seasonal flows of water. The streaks are roughly the length of a football field. (NASA/JPL-Caltech/Univ. of Arizona)

As a species, before we reach the point where we need to start thinking about the specific technological requirements to harvest water (liquid or frozen) from Mars to support human life, there are still many discoveries to make. Sagan said, "I don't want to believe. I want to know." Knowing requires hard facts and information — concrete proof that cannot be obtained realistically without physical samples. The source of the recurring slope lineae remains unknown. Is it atmospheric, or is it coming from aquifers below Mars' surface? That would have to be determined before we could even begin to speculate about the technological developments necessary to harvest this water. And to do that would require further study and exploration of the regions where the liquid water is found. Ultimately, the recurring slope lineae may not even be the most ideal source of water for any hypothetical human colony. The poles are believed to have large amounts of water, and underwater glaciers are suspected to exist. Future exploration could prove fruitful on that front as well.

The Politics of Further Exploration

International policy here on Earth may delay but not necessarily prevent such future discoveries. A U.N. treaty from the 1960s designates that exploration of celestial bodies must be conducted to avoid harmful contamination of the environment being explored. Specifically on Mars, the Committee on Space Research (COSPAR) has already identified parts of the planet that have a higher possibility of contamination by — and even replication of — terrestrial organisms. Some microbes from Earth have proven remarkably resilient, living on the outside of the International Space Station for more than 500 days. So, potential for growth of Earth-based organisms on Mars is not totally unfounded. The exploration of extreme areas here on Earth, like subglacial Lake Vostok in Antarctica, illustrates the difficulties of preventing contamination. However, while some might interpret the treaty as having an outright ban on the exploration of water on Mars, the language within it is not strong enough to suggest total prohibition. The desire and the need to know will eventually override any objections harbored by the international treaty.

NASA's announcement of probable liquid water on Mars is unlikely to change the goals of the European Space Agency's 2018 mission. Or even the deployment of the next rover, planned for 2020. NASA has already set its main objectives for the Mars rover mission in 2020, and the seven instruments the rover will carry were selected in 2014. Although the areas believed to have liquid water will almost certainly be studied further, and the landing site of the 2020 rover has not yet been determined, the robotic explorer is unlikely to land near the recurring slope lineae. The NASA rover is powered by a generator that contains nuclear material, and landing sites are restricted to areas that do not contain water. Rather, the rover will collect even more information about the planet's surface and weather. NASA hopes to gain more information about the Martian environment, as well as searching for biosignatures that might give further clues about past (or present) life on Mars. The rover also has the objective to cache samples that will eventually be returned to Earth on future missions for further study — a measure some planetary sciences consider a requirement before a manned mission.

Budgetary Considerations

In the short term, it may be budgetary hurdles and debates over necessary mission goals that limit missions to Mars, not international treaties. As with any government program, NASA's objectives on Mars remain constrained by government allocations. In 2012, NASA announced that it would not be participating in parts of a planned joint mission with the European Space Agency to return samples from Mars because of budget cuts. This happened even after the National Research Council designated Mars as a first priority in planetary science missions.

Currently, support for manned Mars missions appears to be higher than some other exploratory goals. In April 2015, the NASA Advisory Council suggested that the Asteroid Redirect mission be changed to focus less on robotic retrieval and more on the high-powered solar electric propulsion spacecraft that could be used in Mars missions. They even indicated that the mission could target Mars' moon Phobos. Yet, budgets and political support are often administration-dependent, and priorities could change as early as 2017, when the next U.S. president takes the oath of office.

Though curtailed by their own sets of constraints, private companies are not held back by governmental funding or the whims of changing administrations. Many private companies have their eyes set on Mars — specifically, with the purpose of delivering a human payload. Piggybacking on many of the national programs' basic discoveries, these private companies can focus on the flashy, investment-attracting goal of putting a human on Mars. But to meet ambitious mission schedules — according to which, Mars One or SpaceX could put a person on Mars before NASA — these companies will have to change their strategies. They will have to move beyond modernizing and optimizing existing technology and begin investing in their own research in order to complete their desired goals.

The timeline of a manned mission to Mars is subject to change, but when the first humans set foot on the red planet, what will be there to welcome them? The child inside us may hope for Bugs Bunny's nemesis Marvin, but that will probably not be the case. One last quote from Carl Sagan seems appropriate here, addressing what happens if we discover life on Mars. He said, "Mars then belongs to the Martians, even if the Martians are only microbes."

Sagan pushed for the scientific ideal of leaving Mars as its future explorers find it — relatively unsullied by humankind. Still, after our great curiosity allows us to travel there and examine its secrets in person, there will be an inevitable impact. Putting boots on the Martian ground will likely change the environment, violating a treaty that may have lost its meaning even before this point. As we discover more about the Martian surface, we will further understand what technological breakthroughs will be necessary for us to prevail there. The timeline may change, but we will get there eventually, whether the motivation is from continued curiosity or ensuing necessity. And once the human race arrives, colony or otherwise, its presence will be enduring, if only on the microbial scale.